304 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



give results which agree, in the main, with each other. In 

 making use of the tables given by Professor Whitney, the 

 most that can be hoped for is a better agreement among 

 themselves of the altitudes computed from observations 

 taken in different conditions of the atmosphere. Whitney's 

 Contributions to Barometric Hypsometry, p. 42. 



THE STADIOMETEE. 



The stadiometer is the name given by Captain Bellomayer 

 to an instrument invented by him, which is intended to give 

 by one simple reading the length of any line whatever 

 straight, broken, or curved as drawn on charts and plans 

 executed on all kinds of scales. The principle of its con- 

 struction is quite simple. A toothed steel wheel rolling 

 along over the given line makes an endless screw move by 

 means of a pinion. Upon the screw a slider, held in place 

 by friction, is then forced to rise or fall. The graduations 

 are marked upon two faces of the instrument, on the right 

 and left of the slider. The instrument carries eight scales, 

 corresponding to the scales of the French, Prussian, Belgian, 

 Italian, and other national charts, together with the scale 

 corresponding to the natural scale of our meter. Other 

 scales which are less frequently used may be derived from 

 those which are engraved on the instrument. In using the 

 instrument it is held at right angles to the chart, the toothed 

 wheel pressing against the surface of the latter. As the 

 wheel is rolled along over a given line, the slider is, by 

 means of the endless screw, pushed along the graduated 

 scale of the instrument, and the quantity of its movement 

 as shown thereon gives the exact line to be measured on the 

 chart. The principle of the stadiometer has been for a long 

 time known and used. For many years the French Depot 

 of Charts and Plans has been accustomed to pay its en- 

 gravers according: to the total length of the curved lines 

 which they trace, measuring these lengths by means of 

 wheels rollimr alone: over the lines; but the instrument de- 

 vised by Captain Bellomayer replaces these elementary de- 

 vices by a very portable, convenient, and precise instru- 

 ment. 13 I?, ILL, 203. 



